Transparent conductive film materials in use today are predominantly inorganic oxides such as indium tin oxide (ITO) and indium zinc oxide (IZO). These are standard materials that have good optical clarity and electrical conductivity. However, complex processes such as sputtering and high-vacuum, high-temperature annealing are required to obtain such inorganic oxide films. Hence, there is a need for special equipment, which is costly.
As electronic devices become increasingly flexible and lightweight owing to the use of, for example, plastic substrates, there has arisen a need for durability to physical stress from bending and the like. Although ITO and IZO film-forming technology on flexible substrates is also under investigation, the inherent brittleness and fragility of inorganic oxides have yet to be improved.
In recent years, such progress toward greater flexibility has been accompanied by the development of transparent conductive films having conductive nanostructures (such as metal nanoparticle or metal nanowire percolation structures or metal mesh structures). Using a metal nanoparticle or metal nanowire dispersion, transparent conductive films can be produced by wet processes (Patent Documents 1 to 3).
It is possible to lower the electrical resistance of a transparent conductive film having electrically conductive nanostructures merely by increasing the amount of metal included; that is, without requiring a complex process. However, increasing the amount of metal gives rise to clouding on account of the irregular reflection of light, resulting in a loss of optical clarity. In addition, problems associated with the use of metal include a loss of electrical conductivity due to surface deterioration or breakup of the nanostructures.